The following text should not be construed as an admission of knowledge in the prior art. Furthermore, citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention, or that any reference forms a part of the common general knowledge in the art.
Pain can be caused by a variety of diseases and injuries. A significant difficulty in the treatment of pain is properly diagnosing the cause of the pain. That is, once a physician has identified the nature of the pain, treating the pain or the cause of the pain can be more successful than attempting to treat the pain or the cause of the pain if the physician cannot accurately identify the nature of the patient's pain. Thus, if the treating physician cannot first correctly identify the nature of the patient's pain, the physician may try to treat the pain in a manner that will not bring relief to the patient because the pain has a different source than the false source identified by the physician. For example, if a patient is experiencing pain in his or her shoulder, the pain could be caused by scar tissue from a prior surgery performed in the proximity of the patient's rotator cuff. Here, the mechanical action of the patient's rotator is impaired by the scar tissue, thereby causing inflammation in the vicinity of the rotator cuff and associated pain. To treat the patient's pain, the physician may adequately address the pain by a surgical procedure to remove the scar tissue. On the other hand, if the patient's pain is caused by nerve damage, removing or attempting to remove scar tissue will not necessarily bring the patient any relief from the pain. Indeed, the patient may ultimately experience more pain because of undergoing the surgical procedure, which could possibly lead to other complications. In contrast, if the treating physician were to have properly identified that the cause of the patient's pain was a neurological source, then such recurring pain may have been properly addressed using another treatment, such as neurostimulation.
It is generally accepted that there are two main types of pain. One type of pain is called nociceptive pain, and this type of pain is the normal physiological pain that is associated with a warning signal that something is threatening the person's bodily tissues. Therefore, nociceptive pain serves to alert or signal a person that appropriate measures can possibly be taken to avoid or mitigate further tissue damage. Nociceptive pain is transmitted through the spino-thalamic tract and is the type of pain that people normally experience from a disease or injury. Thus, by way of example, nociceptive pain occurs after mechanical, chemical, and/or thermal stimulation of A-delta and C-polymodal pain receptors. Examples of nociceptive pain are sprains and/or strains, broken bones, lower back pain from disc disease or injury, and burns.
In contrast, neuropathic pain is pain that is caused by damage to the person's nervous system. Neuropathic pain is pain that a person experiences due to transmission of pain signals in the absence of actual tissue damage. However, neuropathic pain can also be a sequela of nociceptive pain if damage to the nervous tissue also occurred with an injury. Thus, with neuropathic pain, the nerve fibers themselves may be damaged or injured and send signals that are interpreted by the person's brain as pain. Neuropathic pain often becomes chronic and lasts over 6 months, and can also become a permanent condition. When this occurs, the neuropathic pain serves no real protective biological function, because it is not serving to warn the person of an injury to allow the person to act to avoid further harm. Rather, the neuropathic pain is the problem itself. Thus, rather than being the symptom of a disease or a warning of injury, the chronic neuropathic pain is itself the disease. With neuropathic pain, the pain the person is experiencing is real, but it is not useful because the person cannot take action to remedy or mitigate a disease or injury. Examples of neuropathic pain include instances when a patient experiences sensations described as hot, cold, shocking, burning, electrical or numbness, and where the pain is attributable to a non-injury source, such as shingles, thalamic stroke, and diabetic neuropathy.
The treatment for nociceptive pain is to remove the offending cause. The pain will automatically disappear. Thus, nociceptive pain can be cured. In contrast, neuropathic pain cannot be cured. The goal of the treatment for neuropathic pain is to try to decrease the pain. Often times a patient will have a mixed condition, where both types of pain coexist in different percentages.
It is, therefore, important to try to distinguish nociceptive pain from neuropathic pain so that the appropriate treatment can be formulated. More surgical interventions on someone with neuropathic pain will inevitably lead to failure and further pain. Unfortunately, often the situation is not so clear, and it might be difficult to separate the two types of pain. Complicating this issue is that nociceptive pain and neuropathic pain can often coexist. Sometimes the nociceptive component is dominant, other times the neuropathic component is the prevalent one.
Descriptors exist in the literature that characterize the two types of pain. However, unless a physician is truly experienced in the pain field, a true differentiation might be difficult. Often times the physician does not ask the proper questions or does not correctly assess the answers. Pain scales currently available assess the severity of the pain, the verbal descriptors of the pain, and the impact of the pain on the psychological and social milieu of the patient.
One such method is known as the Visual Analogue Rating scale (“VAS”). See Huskisson, “Measurement of Pain,” Lancet, 1974; 2:1127-1131, the content of which is incorporated herein by reference. VAS may be the most widespread pain intensity measurement scale. However, VAS does not differentiate between types of symptoms, but purely assigns a numerical value to the intensity of the pain.
A second method of describing pain is the McGill Pain Questionnaire (“MPQ”). See Melzack, “The McGill Pain Questionnaire: Major Properties and Scoring Methods,” Pain, 1975, 1:277-299, the content of which is incorporated herein by reference. The MPQ incorporates a series of adjectives to describe the characteristics and intensity of a patient's pain. In addition, the MPQ uses a mannequin to allow the patient draw the areas of pain. The MPQ is used to specify subjective pain experience using sensory, affective and evaluative word descriptors. There are three major measures: the pain rating index, based on two types of numerical values that can be assigned to each word descriptor; the number of words chosen; and the present pain intensity based on a 1-5 intensity scale. The MPQ was developed to indicate the extent of change in pain quality and intensity as a result of an intervention.
Yet another method of describing pain is the Wisconsin Brief Pain Questionnaire (“BPQ”). BPQ is described as a self-administered instrument that assesses pain. The BPQ uses a human figure that is shaded to indicate pain, rating of pain intensity, relief from medication, and ratings of pain interference. A 0-4 scale is used. The BPQ was used as an outcome measure in a study of pain in ambulatory HIV patients. See McCormack et al., “Inadequate Treatment of Pain in Ambulatory HIV Patients,” Clin. J. Pain, 1993, 9:279-83. The study was able to show that pain control in this population is inadequate with usual intervention. The BPQ has been used in cancer, rheumatoid arthritis and HIV patients. See Daut et al., “Development of the Wisconsin Brief Pain Questionnaire to Assess Pain in Cancer and Other Diseases, Pain, 1983, 17:197-210, the content of which is incorporated herein by reference.
The Battery for Health Improvement 2 (“BHI 2”) is described as an assessment of the biopsychosocial issues that are relevant in evaluating medical patients. The BHI 2 test is described as being able to help caregivers shape an appropriate treatment plan, reduce treatment time and improve a patient's quality of life.
Still another method of describing pain is the Minnesota Multiphasic Personality Inventory-2 (“MMPI-2”). The MMPI-2 is a test of adult psychopathology and is used by clinicians to assist with the diagnosis of mental disorders and the selection of appropriate treatment methods. The MMPI-2 test is described as being able to help assess medical patients and design effective treatment strategies, including chronic pain management. However, MMPI-2 does not have any questions related to nociceptive pain symptoms and does not allow a differentiation between the two types of pain.
Yet another method of describing pain is the Neuropathic Pain Scale (“NPS”). The NPS is described as being able to measure the intensity of different symptoms that are associated with neuropathic pain. However, NPS does not have any questions related to nociceptive pain symptoms and does not allow a differentiation between the two types of pain.
Although some prescribed drugs can be helpful for addressing neuropathic pain, certain individuals can have difficulties with various side effects associated with pain relieving drugs. Neurostimulation is a method that can be used for treating chronic neuropathic pain. Accordingly, in some instances, electrical stimulation of nerves within the body can be used to control pain of a patient suffering from chronic neuropathic pain. However, to properly treat the neuropathic pain, the physician must first be able to diagnose that the pain originates from a neurological source, and herein lies the problem because the cause of a person's pain is not necessarily easy to discover.
Accordingly, it would be beneficial to have a method of properly identifying the nature of the patient's pain so that the treating physician can undertake steps to properly treat the patient, thereby providing the patient relief. In addition, it would be advantageous to provide a system for assisting a physician to identify whether a patient's pain is nociceptive pain or neuropathic pain, and it would be help to also provide a process for assisting a physician to distinguish nociceptive pain from neuropathic pain using information provided by a patient.
Nothing herein is to be construed as an admission that the present invention is not entitled to antedate a publication by virtue of prior invention. Furthermore, the dates of publication where provided are subject to change if it is found that the actual date of publication is different from that provided here.